The present invention relates to an improved sub-surface geothermal direct exchange (also commonly referred to as “direct expansion”) tubing installation means, comprising situating certain sized refrigerant transport sub-surface tubing within each of a horizontally oriented trench and a vertically oriented well/borehole, so as to provide a highly efficient sub-surface heat transfer means, when sufficient land surface area is available, at a lower cost than with a primarily vertically oriented tubing installation means. Further, the present invention relates to a means to increase the efficiency of any direct exchange system design by means of adding an additional liquid refrigerant transport line segment in at least one of a vertically oriented well/borehole and a horizontally oriented trench and/or pit, as well as to a means of improving the efficiency and durability of horizontally oriented sub-surface refrigerant transport heat exchange tubing by utilizing a refrigerant with a higher operating pressure than R-22 and by surrounding the refrigerant transport tubing with a protective solid grout.
Geothermal ground source/water source heat exchange systems typically utilize fluid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged fluid transport tubing. The tubing loop is extended to the surface and is then used to circulate one of the naturally warmed and naturally cooled fluid to an interior air heat exchange means.
Common and older design geothermal water-source heating/cooling systems typically circulate, via a water pump, a fluid comprised of water, or water with anti-freeze, in plastic (typically polyethylene) underground geothermal tubing so as to transfer heat to or from the ground in a first heat exchange step. Via a second heat exchange step, a refrigerant is utilized to transfer heat to or from the water. Finally, via a third heat exchange step, an electric fan is utilized to transfer heat to or from the refrigerant to heat or cool interior air space.
Newer design Direct eXchange/Direct eXpansion (“DX”) geothermal heat exchange systems, where the refrigerant fluid transport lines are placed directly in the sub-surface ground and/or water, typically circulate a refrigerant fluid, such as R-22 or the like, in sub-surface refrigerant lines, typically comprised of copper tubing, to transfer heat to or from the sub-surface elements via a first heat exchange step. DX systems only require a second heat exchange step to transfer heat to or from the interior air space, typically by means of an electric fan. Consequently, DX systems are generally more efficient than water-source systems because of less heat exchange steps and because no water pump energy expenditure is required. Further, since copper is a better heat conductor than most plastics, and since the refrigerant fluid circulating within the copper tubing of a DX system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system, generally, less excavation and drilling is required, and installation costs are lower, with a DX system than with a water-source system.
While most in-ground/in-water heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements, particularly in direct expansion/direct exchange geothermal heat pump systems, are taught in U.S. Pat. No. 5,623,986 to Wiggs; in U.S. Pat. No. 5,816,314 to Wiggs, et al.; in U.S. Pat. No. 5,946,928 to Wiggs; and in U.S. Pat. No. 6,615,601 B1 to Wiggs, the disclosures of which are incorporated herein by reference. Such disclosures encompass both horizontally and vertically oriented sub-surface heat geothermal heat exchange means.
Historically, DX systems, with principally horizontally oriented geothermal heat exchange means, utilized an array of multiple smaller diameter tubing, typically comprised of at least one of ⅛″, ¼″, and ⅜″ tubing in a horizontally inclined manner, all connecting to a principal single vapor refrigerant transport line at one end and to a principal single liquid refrigerant transport line at the other end. Also, horizontally oriented designs have been tested by Wiggs utilizing at least one long heat exchange transport tube within a long horizontally oriented near-surface trench. Typically, horizontally oriented DX systems are the least expensive to install because excavation can be accomplished with only a backhoe and/or a front-end loader.
Also historically, DX systems, with principally vertically oriented geothermal heat exchange means, utilized at least one well/borehole within which to insert a closed loop of refrigerant transport heat exchange tubing. Generally, because of extreme and fluctuating hot/cold atmospheric effects upon ground in close proximity to the surface, DX systems within a well/borehole have historically been more efficient, even though they have typically been the most expensive to install because of well-drilling costs.
Since combining the less expensive horizontally oriented heat exchange tubing with the more efficient vertically oriented heat exchange tubing would provide a more affordable system than a solely vertical installation and a more efficient system than a solely horizontal installation, an appropriate combination design would be preferable for many applications. Also, such a combination design, that provided very high operational efficiencies, would be preferable so as to provide DX system availability to those with limited financial resources and with some, but limited (not enough for a solely horizontal design), available land surface area.
Consequently, a means to provide a highly efficient, and reasonably priced, manner in which to install a combined horizontally and vertically oriented geothermal DX heat exchange fluid transport tubing system that achieved high operational efficiencies would be preferable. Further, a means to supplement and improve the efficiency levels of conventional, and new, horizontally oriented DX system sub-surface heat transfer tubing system designs would also be preferable. The present invention provides a solution to these preferable objectives, as hereinafter more fully described.